Relationships between polypyrrole synthesis conditions, its morphology and electronic structure with supercapacitor properties measured in electrolytes with different ions and pH values

Abstract

Despite a large number of articles about synthesis methods, structure, morphology and electrochemical properties of polypyrrole, none of these works reports the relationships between polypyrrole synthetic conditions, the electronic states of atoms in the polymer chains and its electrochemical properties in various electrolytes. Our work is dedicated to filling part of this gap. This work is focused on the effect of the synthetic medium used for polypyrrole synthesis on their atomic and electronic structure and morphology as well as investigation of the influence of these on the electrochemical characteristics of polypyrrole in aqueous electrolytes with different ions and pH values within a supercapacitor setup. It is shown that synthetic medium does not affect polymer particle shapes but changes particle sizes. Using oxygen functional groups containing synthetic medium based on water and ethanol leads to a decrease in C:N ratio, increase in C:O ratio, increase in the concentration of positively charged nitrogen-species and formation of linear-structured polymer chains. Contrary, acetonitrile-based synthetic medium without oxygen-containing functional groups leads to an increase in C:N ratio and concentration of neutrally charged nitrogen species, decrease in C:O ratio and formation of branched-structured polymer chains. Electrochemical properties of polypyrrole depend on the nature of the electrolyte, then nitrogen species and oxygen-containing functional groups in polypyrrole structure, and the size of polypyrrole particles. The favorable electrolyte for using polypyrrole in supercapacitors is neutral. The specific capacitance of polypyrrole produced in acetonitrile is shown to reach the value of ~ 385 F g −1 which is stable for more than 10,000 cycles in 1M KCl aqueous solution.